Detect malicious inbox/mail-flow forwarding rules that adversaries create to maintain persistent access to email communications for intelligence collection and business email compromise. Use when hunting for suspicious auto-forwarding, hidden mailbox rules, or T1114-style email collection persistence after a compromised account or BEC incident.
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Use detecting-email-forwarding-rules-attack to develop a threat-hunting plan for [incident or hypothesis] using [available SIEM and EDR telemetry], with detection queries, validation steps, and response recommendations.
Required inputs
[incident or hypothesis]
[available SIEM and EDR telemetry]
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SKILL.md
name: detecting-email-forwarding-rules-attackdescription: Detect malicious inbox/mail-flow forwarding rules that adversaries create to maintain persistent access to email communications for intelligence collection and business email compromise. Use when hunting for suspicious auto-forwarding, hidden mailbox rules, or T1114-style email collection persistence after a compromised account or BEC incident.domain: cybersecuritysubdomain: threat-huntingtags: - threat-hunting- mitre-attack- email-forwarding- persistence- bec- t1114- proactive-detectionversion: '1.0'author: mahipallicense: Apache-2.0d3fend_techniques: - Restore Object- Restore Configuration- Application Configuration Hardening- Application Hardening- Disable Remote Accessnist_csf: - DE.CM-01- DE.AE-02- DE.AE-07- ID.RA-05mitre_attack: - T1046- T1057- T1082- T1083- T1547
Detecting Email Forwarding Rules Attack
When to Use
When proactively hunting for indicators of detecting email forwarding rules attack in the environment
After threat intelligence indicates active campaigns using these techniques
During incident response to scope compromise related to these techniques
When EDR or SIEM alerts trigger on related indicators
During periodic security assessments and purple team exercises
Prerequisites
EDR platform with process and network telemetry (CrowdStrike, MDE, SentinelOne)
SIEM with relevant log data ingested (Splunk, Elastic, Sentinel)
Sysmon deployed with comprehensive configuration
Windows Security Event Log forwarding enabled
Threat intelligence feeds for IOC correlation
Workflow
Formulate Hypothesis: Define a testable hypothesis based on threat intelligence or ATT&CK gap analysis.
Identify Data Sources: Determine which logs and telemetry are needed to validate or refute the hypothesis.
Execute Queries: Run detection queries against SIEM and EDR platforms to collect relevant events.
Analyze Results: Examine query results for anomalies, correlating across multiple data sources.
Validate Findings: Distinguish true positives from false positives through contextual analysis.
Correlate Activity: Link findings to broader attack chains and threat actor TTPs.
Document and Report: Record findings, update detection rules, and recommend response actions.
Key Concepts
Concept
Description
T1114.003
Email Forwarding Rule
T1114.002
Remote Email Collection
T1098.002
Additional Email Delegate Permissions
Tools & Systems
Tool
Purpose
CrowdStrike Falcon
EDR telemetry and threat detection
Microsoft Defender for Endpoint
Advanced hunting with KQL
Splunk Enterprise
SIEM log analysis with SPL queries
Elastic Security
Detection rules and investigation timeline
Sysmon
Detailed Windows event monitoring
Velociraptor
Endpoint artifact collection and hunting
Sigma Rules
Cross-platform detection rule format
Common Scenarios
Scenario 1: BEC actor creating forwarding rule to external email
Scenario 2: Compromised account with rule deleting security alerts
Scenario 3: Inbox rule forwarding CEO emails to attacker mailbox
Scenario 4: OAuth app abuse creating transport rules for data collection